English

Graphs with $\alpha_1$ and $\tau_1$ both large

Combinatorics 2018-05-08 v2

Abstract

Given a graph GG, let τ1(G)\tau_1(G) denote the smallest size of a set of edges whose deletion makes GG triangle-free, and let α1(G)\alpha_1(G) denote the largest size of an edge set containing at most one edge from each triangle of GG. Erd\H{o}s, Gallai, and Tuza introduced several problems with the unifying theme that α1(G)\alpha_1(G) and τ1(G)\tau_1(G) cannot both be "very large"; the most well-known such problem is their conjecture that α1(G)+τ1(G)V(G)2/4\alpha_1(G) + \tau_1(G) \leq |V(G)|^2/4, which was proved by Norin and Sun. We consider three other problems within this theme (two introduced by Erd\H{o}s, Gallai, and Tuza, another by Norin and Sun), all of which request an upper bound either on min{α1(G),τ1(G)}\min\{\alpha_1(G), \tau_1(G)\} or on α1(G)+kτ1(G)\alpha_1(G) + k\tau_1(G) for some constant kk, and prove the existence of graphs for which these quantities are "large".

Keywords

Cite

@article{arxiv.1705.04745,
  title  = {Graphs with $\alpha_1$ and $\tau_1$ both large},
  author = {Gregory J. Puleo},
  journal= {arXiv preprint arXiv:1705.04745},
  year   = {2018}
}

Comments

6 pages; improved exposition a bit and fixed an issue regarding integrality from the earlier version

R2 v1 2026-06-22T19:45:52.518Z